This invention relates to a labelling machine having a label box for a stack of labels in a labelling station with at least one extractor element located on a turntable so that the extractor element can rotate or pivot. The extractor element, with its convexly curved pickup surface to which adhesive can be applied by an adhesive application device, can be rolled past the end surface of the stack of labels. To guide the stack of labels, there are guide elements which are located on the sides and bottom of the stack and which extend to the front side of the stack. The stack of labels can be pushed, on one hand, from its back side and, on the other hand, on its front side by holding elements which overlap the edge of the stack, and with a regulating device, which device transfers the label box together with the labels in it from the rolling contact position on the front side of the stack into a retracted idle position.
With a label box which can move forward and backward, it is possible to precisely control the extraction of the label from the stack of labels and thus also the transfer of the label to the object to be labelled. This control is carried out so that no label is extracted if, on account of the absence of an object to be labelled in a series, it is not possible to transfer a label. Without this control, in the absence of an object to be labelled, a label would still be extracted, but that would lead to disruptions in the further extraction and transfer of the label, because the label extracted from the label stack but not transferred to the object to be labelled would be covered by a new label taken from the stack.
As a solution for this requirement, to prevent the extraction of a label from the stack by the extractor element, the former designs include not only the backward movement of the entire label box, but also the activation of holding elements which act on the end surface of the label stack or additional holding elements, so that the pressure exerted by them on the end surface of the label stack and the related compression on at least the front edge of the label stack in the rolling contact direction reduces the contact pressure of the rolling pickup surface, so that the adhesive force of the adhesive is not sufficient during the rolling process to extract the forward label from the stack. In this solution, in contrast to the first solution with the adjustable label box, the label box is not moved. Rather, this solution is based on the principle that the holding elements hold the labels so tight that in spite of the full-contact rolling of the pickup surface of the extraction element on the end surface of the label stack, the label cannot be extracted. In the extreme case, however, it is also possible to activate all the holding elements so strongly that the end surface of the label stack is moved back so far that the pickup surface of the extractor element no longer contacts the end surface. In this case, considerable effort is required to activate and control the many holding elements (German Patent Application No. 32 45 879 C2).
In another former labelling machine, each holding element designed as a small hook overlapping the front edge of the label stack, does not have its own hydraulic or pneumatic cylinder, but the small hooks are guided in guide rails so that the hooks can move along the label box, and can be coupled to one another by means of a frame for joint movement by means of a hydraulic cylinder. In this solution, the guide rails end shortly in front of the front side of the stack. That means that there is no precise guidance in exactly the area in which a precise extraction of labels from the stack is necessary (German Patent No. 21 39 662).